1. Field of the Invention
The invention relates to a variable inductor, and particularly to a variable inductor suitable for use with various high-frequency or microwave circuits.
2. Description of the Related Art
In the family of electronic devices, the existence of variable inductors makes the fabrication of electronic circuits more flexible and convenient. Variable inductors have been widely used in electronic circuits having operating frequencies below hundreds of megahertz (MHz), such as the matching circuit, the tuning circuit, and so on. However, conventional variable inductors are incapable of acting as inductors at high operating frequencies; their frequency characteristics are poor, and the value of the quality factor Q is extremely low. Therefore, conventional variable inductors cannot be used for electronic circuits having high operating frequencies.
Chinese Patent No. 200410027166.9 discloses a variable inductor suitable for high-frequency or microwave circuits, comprising a substrate, a fixed inductor, and signal terminals made of metal microstrip line disposed on the substrate, which also comprises 1) a conductive sheet disposed on the substrate for changing the geometry of the metal microstrip line of the effective inductance portion of the fixed inductor, 2) and an insulator for changing the contact area between the conductive sheet and the metal microstrip line of the fixed inductor, the insulator being adjacent to the conductive sheet.
However, a variable inductor may only operate within a certain range; in case that a number of inductance values are required, it is difficult to efficiently adjust and obtain the required inductance values.